Granulocyte colony-stimulating factors, such as recombinant granulocyte colony-stimulating factor (rG-CSF), have been known in the prior art as humoral factors that stimulate differentiation and proliferation of granulocytes. Reports based on in vivo experiments with mice have shown that administration of rG-CSF results in not only accelerated myelopoiesis in bone marrow but also notable extramedullary hemopoiesis in the spleen, and proliferation of all hemopoietic precursor cells, including hemopoietic stem cells, in the spleen. The mechanism of such extramedullary hemopoiesis in the spleen has been believed that stimulation by rG-CSF alters the hemopoietic microenvironment of the spleen and promotes the hemopoiesis supporting ability thereof, thus inducing hemopoiesis.
In order to elucidate the hemopoietic function in the spleen, the present inventors have previously focused on stromal cells of the spleen following repeated administration of rG-CSF. The inventors have made efforts to examine how the hemopoietic function is promoted by rG-CSF via stromal cells, and have established a hemopoietic stromal cell line (CF-1 cells) from mouse spleen by repeated administration of rG-CSF. The inventors have studied the hemopoiesis-supporting ability of the hemopoietic stromal cells and confirmed the colony-stimulating activity in vitro and the hemopoietic stem cell-supporting ability in vivo [Blood, 80, 1914 (1992)].
However, while one cell line of the splenic stromal cells has been established (CF-1 cells) and its cytological characteristics have been studied, specific antibodies that recognize the surface antigens of these cells have never been prepared, nor have their characteristics been elucidated yet in any way.